Low Oxygen Pressure Research Articles

Phase transitions involving Ca – The most abundant ash forming element – In thermal treatment of lignocellulosic biomass

Torrefaction, pyrolysis and gasification are of interest to convert lignocellulosic biomass into fuels and chemicals. These techniques involve thermal treatment at low partial pressures of oxygen. However, little is known about the transformation of ash elements during these processes. The phase transition of the major ash element calcium (Ca) was therefore studied with powder from pine as biomass model treated at temperatures 300–800 °C under atmospheres of 100% N2, 3% O2 and 6% O2 and thermodynamic equilibrium modelling. For evaluation, X-ray powder diffraction and synchrotron Ca K-edge X-ray absorption near edge structure (XANES) spectroscopy in combination with linear combination fitting and reference compounds was used.The results indicated that the most abundant Ca-containing species in the untreated material was thermally unstable Ca oxalate (CaC2O4) primarily decomposing into Ca phases dominated by carbonates at temperatures up to 600 °C. Double carbonates of calcium and potassium were observed in the form of fairchildiite/butscheliite (K2Ca(CO3)2), and these phases were stable over the low temperature range studied. Hydroxyapatite (Ca5(PO4)3OH) was expected to be present and thermally stable over the entire temperature interval and was found in untreated material. At temperatures above 600 °C calcium oxide (CaO) was formed. The amount of oxygen had little effect on the phase transitions. The results of thermodynamic modeling were in agreement with XANES showing that this is a versatile technique that can be applied to systems as complex as Ca phase transitions in thermally treated lignocellulosic biomass at low partial pressures of oxygen.

Maintaining a high inspired oxygen fraction with the Elisée 350 turbine transport ventilator connected to two portable oxygen concentrators in an austere environment.

Management of critically ill patients requiring mechanical ventilation in austere environments or during disaster response is a logistic challenge. Availability of oxygen cylinders for mechanically ventilated patient may be difficult in such a context. A solution to ventilate patients requiring high fraction of inspired oxygen (FiO2) is to use a ventilator able to be supplied by a low-pressure oxygen source connected with two oxygen concentrators (OCs). We tested the Elisée 350 (ResMedBella Vista, Australia) ventilator paired with two Newlife Intensity 10 (Airsep, Ball Ground, Georgia) OCs and evaluated the delivered FiO2 across a range of minute volumes and combinations of ventilator settings. The ventilators were attached to a test lung, OC flow was adjusted with a Certifier FA ventilator test systems from 2 to 10 L/min and injected into the oxygen inlet port of the Elisée 350. The FiO2 was measured by the analyzer integrated in the ventilator, controlled by the ventilator test system. Several combinations of ventilator settings were evaluated to determine the factors affecting the delivered FiO2. The Elisée 350 ventilator is a turbine ventilator able to deliver high FiO2 when functioning with two OCs. However, modifications of the ventilator settings such as an increase in minute ventilation affect delivered FiO2 even if oxygen flow is constant on the OC. The ability of two OCs to deliver high FiO2 when used with a turbine ventilator makes this method of oxygen delivery a viable alternative to cylinders to ventilate patients requiring an FiO2 of ≥80% in austere place or during disaster response. Feasibility study on test bench, level V.

Utilization of machine-learning models to accurately predict the risk for critical COVID-19.

Among patients with Coronavirus disease (COVID-19), the ability to identify patients at risk for deterioration during their hospital stay is essential for effective patient allocation and management. To predict patient risk for critical COVID-19 based on status at admission using machine-learning models. Retrospective study based on a database of tertiary medical center with designated departments for patients with COVID-19. Patients with severe COVID-19 at admission, based on low oxygen saturation, low partial arterial oxygen pressure, were excluded. The primary outcome was risk for critical disease, defined as mechanical ventilation, multi-organ failure, admission to the ICU, and/or death. Three different machine-learning models were used to predict patient deterioration and compared to currently suggested predictors and to the APACHEII risk-prediction score. Among 6995 patients evaluated, 162 were hospitalized with non-severe COVID-19, of them, 25 (15.4%) patients deteriorated to critical COVID-19. Machine-learning models outperformed the all other parameters, including the APACHE II score (ROC AUC of 0.92 vs. 0.79, respectively), reaching 88.0% sensitivity, 92.7% specificity and 92.0% accuracy in predicting critical COVID-19. The most contributory variables to the models were APACHE II score, white blood cell count, time from symptoms to admission, oxygen saturation and blood lymphocytes count. Machine-learning models demonstrated high efficacy in predicting critical COVID-19 compared to the most efficacious tools available. Hence, artificial intelligence may be applied for accurate risk prediction of patients with COVID-19, to optimize patients triage and in-hospital allocation, better prioritization of medical resources and improved overall management of the COVID-19 pandemic.

Ambient-pressure endstation of the Versatile Soft X-ray (VerSoX) beamline at Diamond Light Source.

The ambient-pressure endstation and branchline of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source serves a very diverse user community studying heterogeneous catalysts, pharmaceuticals and biomaterials under realistic conditions, liquids and ices, and novel electronic, photonic and battery materials. The instrument facilitates studies of the near-surface chemical composition, electronic and geometric structure of a variety of samples using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the photon energy range from 170 eV to 2800 eV. The beamline provides a resolving power hν/Δ(hν) > 5000 at a photon flux > 1010 photons s-1 over most of its energy range. By operating the optical elements in a low-pressure oxygen atmosphere, carbon contamination can be almost completely eliminated, which makes the beamline particularly suitable for carbon K-edge NEXAFS. The endstation can be operated at pressures up to 100 mbar, whereby XPS can be routinely performed up to 30 mbar. A selection of typical data demonstrates the capability of the instrument to analyse details of the surface composition of solid samples under ambient-pressure conditions using XPS and NEXAFS. In addition, it offers a convenient way of analysing the gas phase through X-ray absorption spectroscopy. Short XPS spectra can be measured at a time scale of tens of seconds. The shortest data acquisition times for NEXAFS are around 0.5 s per data point.

Guide to Leading a Patient with Symptoms of an Acute Respiratory Infection during a Coronavirus Pandemic (COVID-19)

BACKGROUND: Over 500 viruses and bacteria primarily cause respiratory infections. During COVID-19 pandemic, these respiratory infections remain; i.e., COVID-19 has no ability to suppress these infections from the circulation. Therefore, it is very important to differentiate respiratory infections from COVID-19. Proving the presence of COVID-19 with polymerase chain reaction (PCR) is not evidence that the disease was caused by this virus. Possible options are: First, a random encounter of the virus in the patient’s upper respiratory tract; second, further possible colonization with a coronavirus (or with COVID-19); the third option is to have an infection; and the fourth possibility is to have a disease or COVID-19 upper respiratory infection. Unfortunately, the method with PCR, although it is with high sensitivity and specificity, does not help us to distinguish which of these four possibilities are in question.
 AIM: We aimed to present a guide to leading a patient with symptoms of an acute respiratory infection during a coronavirus pandemic (COVID-19).
 RESULTS: A pandemic of COVID-19 shows that many patients get primary viral pneumonia, but people with normal immune system have no problem recovering. People with reduced immunity die from COVID-19, as opposed to the pandemic influenza virus. It is indirectly concluded that COVID-19 in itself is not very virulent, but it weakens the immunity of those infected who already have some condition and impaired immunity. The available scientific papers show that there is no strong cytokine response, patients have leukopenia and lymphopenia, some patients have a decrease in CD4 T-lymphocytes. From the results of the autopsies available so far, it is clear that there are very few inflammatory cells in the lungs and a lot of fluid domination. Hence, SARS-Cov-2 only somehow speeds up the decline in immunity. The previously published radiographic findings of COVID-19 patients, gave a characteristic findings of the presence of multifocal nodules, described as milky glass, very often localized in the periphery of the lung. Whether it is typical pneumonia, atypical, viral, mixed-type pneumonia, or mycotic pneumonia, it can progress to severe pneumonia. The pneumonia becomes severe when breathing is over 30/min; diastolic pressure below 60 mmHg; low partial oxygen pressure in the blood (PaO2/FiO2 <250 mmHg) (1 mmHg = 0.133 kPa); massive pneumonia, bilateral or multilayered lung X-ray; desorientation; leukopenia; and increased urea.
 CONCLUSION: Patients with COVID-19 placed in intensive care units should be led by a team of anesthesiologists with an infectious disease specialist or an anesthesiologist with a pulmonologist. Critical respiratory parameters should be peripheral oxygen saturation <90%, PaO2/FiO2 ratio 100 or <100, tachycardia above 110/min.

Structural Analysis of Kevlar Fabric Treated with Oxygen Plasma

The purpose of this work was to study the effects of low-pressure oxygen plasma treatment on the surface characteristics of kevlar fabric. For comparison purposes, samples treated with oxygenated plasma were prepared and characterised under different experimental conditions, i.e. a treatment time variation of 10, 30 and 60 minutes under a constant pressure of 4 mBar, using a pulsed current source. We analysed the effects of chemical and physical changes to the surface of the material aiming at improved hydrophilicity attributed to the formation of roughness on the surface of fibres, thus obtaining optimal parameters for future works. Changes in the chemical composition of the surface as well as in the superficial roughness of fibres before and after treatment were determined by FTIR, TGA, XRD and wettability testing. SEM was used as a complementary technique to monitor the changes triggered by the procedures using oxygen plasma.

In situ TEM oxidation study of Fe thin-film transformation to single-crystal magnetite nanoparticles

In this work, we present an in situ transmission electron microscopy (TEM) study of Fe thin films to Fe nanoparticle formation and their oxidation to single-crystal magnetite nanoparticles. Amorphous Fe thin films were prepared by sputtering on TEM carbon grids. The thin Fe films were continuously heated in situ from room temperature to 700 °C under vacuum (4 × 10–4 Pa). With the increase in temperature, the continuity of the thin film starts breaking, and Fe nanoparticle nucleation centers are formed. At 600 °C, the thin film transforms into metallic Fe nanoparticles (NPs) with a small presence of different Fe oxide NPs. Further increase in the temperature to 700 °C resulted in the full oxidation of the NPs (i.e., no core–shell were found). Zero-loss energy filtered diffraction and HRTEM analysis of the lattice spacing reveals that all NPs have fully transformed into single-phase magnetite NPs. The structural study of the magnetite NPs shows that magnetite NPs are free of antiphase domain boundary defects. This work demonstrates that under low partial pressure of oxygen at elevated temperatures a complete oxidation of Fe NPs into magnetite single-crystal nanoparticles can be achieved.

Conditioned medium produced by fibroblasts cultured in low oxygen pressure allows the formation of highly structured capillary-like networks in fibrin gels

Tissue engineering is an emerging and promising concept to replace or cure failing organs, but its clinical translation currently encounters issues due to the inability to quickly produce inexpensive thick tissues, which are necessary for many applications. To circumvent this problem, we postulate that cells secrete the optimal cocktail required to promote angiogenesis when they are placed in physiological conditions where their oxygen supply is reduced. Thus, dermal fibroblasts were cultivated under hypoxia (2% O2) to condition their cell culture medium. The potential of this conditioned medium was tested for human umbilical vein endothelial cell proliferation and for their ability to form capillary-like networks into fibrin gels. The medium conditioned by dermal fibroblasts under hypoxic conditions (DF-Hx) induced a more significant proliferation of endothelial cells compared to medium conditioned by dermal fibroblasts under normoxic conditions (DF-Nx). In essence, doubling time for endothelial cells in DF-Hx was reduced by 10.4% compared to DF-Nx after 1 week of conditioning, and by 20.3% after 2 weeks. The DF-Hx allowed the formation of more extended and more structured capillary-like networks than DF-Nx or commercially available medium, paving the way to further refinements.

2-Mercaptobenzimidazole films formed at ultra-low pressure on copper: adsorption, thermal stability and corrosion inhibition performance

2-mercaptobenzimidazole (2-MBI) is considered as an effective corrosion inhibitor for copper. In this study, the adsorption of 2-MBI on pristine and pre-oxidized Cu(111) surfaces was investigated by sublimation at ultra low pressure, using Auger Electron Spectroscopy, Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy in order to understand its corrosion inhibition properties. 2-MBI adsorbs with S and N atoms bonded to Cu. On pristine Cu(111) surface, a self-assembled monolayer is formed at about 5 L, with the adsorption of atomic S resulting from molecule decomposition to form a (7×7)R19.1° structure, and that of the molecule forming a (8 × 8) structure. 2-MBI is lying flat in the adsorbed multilayer. Oxidation of copper prior to exposure results in compact and homogeneous molecular films, with dissociation and substitution of 2D oxide by 2-MBI, but much more slower than that for 2-mercaptobenzothiazole (2-MBT). A multilayer of 2-MBI can block the initial stages of oxidation of copper under low oxygen pressure at room temperature, and the molecular layer is stable until 500°C. The comparison with 2-MBT suggests that the latter is a better corrosion inhibitor for copper at room temperature.

Oxygen saturation and perfusion index screening in neonates at high altitudes: can PDA be predicted?

Screening critical congenital heart disease in neonates with 24-48 h of age could be made by oxygen saturation determination. Perfusion index may be used as an adjunct to pulse oximetry screening to detect non-cyanotic critical congenital heart disease cases such as a left heart outflow obstruction. We evaluate the results of combined screening for oxygen saturation and peripheral perfusion index at high altitudes. The study included 501 neonates older than gestational week 35. The mean oxygen saturation was lower than at sea level, and the screening test was positive in a total of 21 (4.2%) babies. Critical congenital heart diseases were not detected in any patient. A total of 10 (2%) babies were detected with PDA, nine (1.8%) of whom recorded a positive screening test. The prevalence of PDA was significantly higher in the positive screening test group when compared with those who underwent echocardiography due to clinical findings.Conclusion: The median peripheral perfusion index at high altitude was not lower than at sea level, while the mean oxygen saturation, in contrast, was lower than at sea level. The low partial oxygen pressure found at high altitudes leads to a variation in postnatal adaptation and an increased prevalence of PDA. Accordingly, oxygen saturation screening may serve to identify babies with PDA at high altitudes. What is Known: • Oxygen saturation is known to be low at high altitudes, and thus the rates of false positivity are high when screening for critical congenital heart disease. • High altitudes are also associated with an increased prevalence of simple congenital heart disease. What is New: • The peripheral perfusion index at high altitude is not lower than at sea level. • The prevalence of PDA is significantly higher in those with false positive screening results.

1452-P: High-Altitude Polycythemia Is an Independent Risk Factor for Type 2 Diabetes

Background: According to previous researches, there were several risk factors of type 2 diabetes, including age, overweight or obesity, hypertension, dyslipidemia etc. However, it is not clear whether there are specific diabetes related risk factors in high altitude areas due to the unique low oxygen and low atmospheric pressure environment. Methods: This study is a population-based, cross-sectional epidemiological survey. The permanent Tibetan residents in Lhasa and Shigatse were enrolled in this study, including 1 urban area (10 communities) and 7 rural areas (48 villages). OGTT, HbA1c, blood lipid and blood cell counts were measured in all the subjects. Diabetes was diagnosed according to the WHO criteria. The diagnostic standard of high altitude polycythemia (HAPC) is the universal Qinghai standard (male hemoglobin ≥ 210g/L, female ≥ 190g/L). Results: A total of 1401 subjects were enrolled in this study. The average age was 44.3 ± 15.0 years old, 33.3% were male. The prevalence of diabetes in the study population was 3.6% (5.8% among men and 2.6% among women, p=0.003; 4.4% in rural vs. 2.4% in urban areas, p=0.033). The prevalence of diabetes increased with increasing age (1.9%, 4.7%, and 7.1% among persons who were 18 to 44, 45 to 59, and ≥60 years of age, respectively) and with increasing BMI (0, 2.3%, 4.7%, and 11.3% among persons with a BMI of <18.5, 18.5 to 23.9, 24.0 to 27.9, and ≥28.0, respectively). The prevalence of HAPC was 6.4% (6.2% among men and 6.5% among women, p=0.453). The prevalence of diabetes was significantly higher in HAPC group than in non HAPC group (11.2% vs. 3.1%, P<0.001). After quartile grouping of Hb, the prevalence of diabetes was 1.6%, 1.8%, 4.5% and 6.3% respectively (p=0.001). After adjusting for gender, age, BMI, hypertension, hyperuricemia and hypercholesterolemia, logistic regression analysis indicated that HAPC was an independent risk factor for diabetes (or = 3.514, 95% CI 1.606-7.689, P = 0.002). Conclusion: HAPC is an independent risk factor of type 2 diabetes in Tibet, China. Disclosure Q. Ren: None. X. Lv: None. L. Zhou: None. Y. Luo: None. L. Yang: None. L. Ji: None. Funding Science and Technology Project of Tibet Autonomous Region (CGZH2017000085); National Key Research and Development Program (2016YFC1304901)

A method for measuring negative ion density distribution using harmonic currents in a low-pressure oxygen plasma

This work investigates the negative ion density via the floating harmonic method (FHM) in an oxygen inductively coupled plasma (ICP). When a small sinusoidal voltage is applied to the specific potentials of a planar Langmuir probe, harmonic currents will be generated by the sheath nonlinearity. Using harmonic current analysis, it is possible to obtain the positive ion currents, electron currents and electron temperatures within the plasma. One probe potential is set to floating and the other is kept in the range between the floating potential and the plasma potential. From the current ratios of positive ions to electrons, the electronegativity and modified pre-sheath potential can be deduced, thereby obtaining the negative ion density from the quasi-neutrality. The variations in the negative ion density and electronegativity distributions at various gas pressures and applied powers are compared with those of a two-dimensional fluid model incorporating electron heating kinetics and those found using a two-probe method in reference Chabert et al (1999 Plasma Source Sci. Technol. 8 561).

Effects of oxygen partial pressure on the structural and electrical properties of Al and Sb co-doped p-type ZnO thin films grown by pulsed laser deposition

ZnO:Al0.01Sb0.02 thin films were grown on the c-plane sapphire via pulsed laser deposition at 500 °C under different oxygen partial pressures (0.13–66.66 Pa) and their structural and electrical properties were investigated. The thin films deposited under low oxygen partial pressures (0.13–7.99 Pa) grew with a c-axis preferred orientation and a 30° rotated one. At higher oxygen partial pressures (13.33–66.66 Pa), in addition to the main c-axis-oriented domains, partial domains with 32°- and 90°-tilted c-axes were observed. The ZnO:Al0.01Sb0.02 thin films deposited at low oxygen partial pressure and high oxygen partial pressure exhibited n-type and p-type conduction, respectively. The X-ray photoelectron spectroscopy analysis exhibited that the thin films contained more Sb5+ than Sb3+; therefore, the p-type conduction was owing to the Sb5+ ions, which formed the SbZn–2VZn complex.

Microstructure and cyclic oxidation of a Hf-doped (Ni,Pt)Al coating for single-crystal superalloys

A diffusion-barrier-contained Hf-doped (Ni,Pt)Al coating was prepared by firstly composite electroplating and then aluminising. The TEM study of the microstructure showed that Hf serves as a solid solution in (Ni,Pt)Al lattice and forms HfO2 in the Hf-rich zone. This HfO2 is formed in situ during aluminisation under low oxygen pressure. It acts as a diffusion barrier to prevent the inter-diffusion during cyclic oxidation. In comparison with (Ni,Pt)Al coating, the oxide scale on Hf-dope (Ni,Pt)Al is more adherent. Moreover, the surface rumpling extent is much relieved due to slower Al depletion rate and higher creep resistance by Hf addition.

Low oxygen pressure synthesis of NdNiO3-δ nanowires by electrospinning

Synthesis of RNiO3 (R = rare earth) nanowires can be interesting as building blocks with potential applications in optoelectronic devices. Here, we describe the synthesis and characterization of NdNiO3-δ (NNO) nanowires produced by electrospinning technique via polymeric precursor solution at relatively low temperature and oxygen pressure. These NNO nanowires were characterized by x-ray diffraction (XRD), x-ray photodetection spectroscopy (XPS), Field Emission Scanning Electron Microscopy (Fe-SEM), Magnetization (M(T)) and electrical resistance (R(T)) measurements. SEM images revealed a granular nanowire microstructure of NNO nanostructures, with a distribution of nanowire diameters ranging from 50 to 150 nm. The NNO nanowires also exhibit granular characteristics with an average grain diameter of 40 nm. The x-ray diffraction patterns of the NNO nanowires indicated that these samples exhibited a high degree of crystallinity and their Bragg reflections can be indexed to an orthorhombic-distorted (Pbnm symmetry) perovskite structure. The crystalline structure seems to be slightly texturized in some Bragg directions and with a slightly strained crystallite. M(T) and R(T) measurement as a function of temperature curves show that these NNO samples present a metal-insulator (MI) transition close to TMI ∼ 198 K, which is usually observed in NNO thin films and bulk samples. The nanostructured shape and these experimental observations can be promising in designing new electronic devices using this strongly correlated oxide.

Trigonal Cr3+ centers in ferroelectric lead germanate

The fine and hyperfine structures of the paramagnetic resonance spectrum of the trigonal Cr3+ centers in the chromium-doped Pb5Ge3O11 samples after annealing at low oxygen pressure have been studied. The localization of chromium ions in the lead germanate crystal lattice, as well as the results of studying the effect of such doping on the susceptibility of crystals to the second harmonic are discussed.

A theoretical cell-killing model to evaluate oxygen enhancement ratios at DNA damage and cell survival endpoints in radiation therapy

Radio-resistance induced under low oxygen pressure plays an important role in malignant progression in fractionated radiotherapy. For the general approach to predict cell killing under hypoxia, cell-killing models (e.g. the Linear-Quadratic model) have to be fitted to in vitro experimental survival data for both normoxia and hypoxia to obtain the oxygen enhancement ratio (OER). In such a case, model parameters for every oxygen condition needs to be considered by model-fitting approaches. This is inefficient for fractionated irradiation planning. Here, we present an efficient model for fractionated radiotherapy the integrated microdosimetric-kinetic model including cell-cycle distribution and the OER at DNA double-strand break endpoint (OERDSB). The cell survival curves described by this model can reproduce the in vitro experimental survival data for both acute and chronic low oxygen concentrations. The OERDSB used for calculating cell survival agrees well with experimental DSB ratio of normoxia to hypoxia. The important parameters of the model are oxygen pressure and cell-cycle distribution, which enables us to predict cell survival probabilities under chronic hypoxia and chronic anoxia. This work provides biological effective dose (BED) under various oxygen conditions including its uncertainty, which can contribute to creating fractionated regimens for multi-fractionated radiotherapy. If the oxygen concentration in a tumor can be quantified by medical imaging, the present model will make it possible to estimate the cell-killing and BED under hypoxia in more realistic intravital situations.

Geochronology and geochemistry of Neoproterozoic Hamamid metavolcanics hosting largest volcanogenic massive sulfide deposits in Eastern Desert of Egypt: Implications for petrogenesis and tectonic evolution

The Gebel Abu Hamamid area forms the middle part of Shadli Metavolcanics Belt of the South Eastern Desert, which hosts the largest volcanogenic massive sulfide deposits in Egypt. The host-rock succession belongs to the Younger Hamamid Metavolcanics (YHM) group, consisting of mafic and felsic lavas with variable volcaniclastics. Although several studies have attempted to clarify the crustal evolution of the Neoproterozoic basement rocks of the South Eastern Desert, researchers have yet to develop a deep understanding of the petrogenesis, tectonic setting, and ages of these host rocks. In the current study, we newly report whole-rock geochemistry, mineral chemistry, and in-situ U–Pb zircon dating from basaltic to rhyolitic rocks of the YHM group to describe their magmatic evolution. Results indicate that the mafic rocks are characterized by tholeiitic affinity and arc-like geochemical signatures with significantly enriched large-ion lithophile elements and depleted high field strength elements. The parental magma was likely generated by partial melting (~10–15%) of a spinel-lherzolite source mantle that was metasomatized by fluids from a former subduction event, followed by magma ascent under low pressure and low oxygen fugacity conditions. The felsic lavas (~695 Ma) are characterized by subduction-related geochemical characteristics with significant enrichments in Zr, Hf, and Sm. They formed from lithosphere-derived magma enriched by melts from the ancient subducted slab, and later experienced an assimilation-fractional crystallization (AFC) process. The YHM group was formed under extensional geodynamic conditions (back-arc basin setting). The zircon grains display hydrothermal overgrowth at the rims, most likely due to regional metamorphic and hydrothermal changes. This characteristic is likely the effect of hydrothermal fluids associated with the Jurassic-Cretaceous tectonothermal event in the South Eastern Desert.

On the formation of Al2O3 nanofibers during self-propagating high-temperature synthesis of TiO2–Al–C system in various environments

The present study deals with the formation of Al2O3 fibers during self-propagating high-temperature synthesis of the TiO2–Al–C system triggered in argon, oxygen, nitrogen and air environments. Results showed TiC and Al2O3 were the primary products obtained in the argon and oxygen atmospheres. However, the dissolution of nitrogen in the structure of TiC resulted in the formation of Ti(C, N) after synthesis in nitrogen and air environments. Al2O3 fibers just were extensively attained in an air atmosphere with a low partial pressure of oxygen. Long nanofibers were primarily formed at the surface of the compact, while short fibers were developed at the inner part; especially adjacent to the internal pores. The formation mechanism of Al2O3 fibers was proposed as (a) the formation of Al2O gas through reaction of Al with O2 in the environment having low oxygen partial pressure like air; (b) further reaction of Al2O vapor with O2 and the development of Al2O3; and (c) precipitation of Al2O3 in the form of fibers by vapor-solid mechanism.

Optical properties of Si nanocrystals in SiO2 matrix synthesized by reactive pulsed laser deposition

Si ion implantation into SiO2 is widely used to synthesize specimens of SiO2 containing supersaturated Si. We also prepared specimens of supersaturated Si in SiO2 by reactive pulsed laser deposition (PLD) in an oxygen atmosphere. After high temperature annealing of these specimens induces the formation of embedded luminescent Si nanocrystals in SiO2. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to enhance the photoluminescence and to achieve low temperature formation of Si nanocrystals have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluence of 7.5 x 1016 ions/cm2. We also prepared Si nanocrystals embedded in a SiO2 by reactive pulsed laser deposition (PLD) in an oxygen atmosphere by using conventional PLD system with 2nd-harmonic YAG laser (532 nm, 10 Hz, 80 J/cm2) under controlled low oxygen pressure. Samples were subsequently irradiated with an excimer-UV lamp. After the process, the samples were rapidly thermal annealed before furnace annealing (FA). Photoluminescence spectra were measured at various stages at the process. We found that the luminescence intensity is enhanced with excimer-UV irradiation and RTA. Moreover, effective visible photoluminescence is found to be observed even after FA below the annealing temperature at 1000 °C, only for specimens treated with excimer-UV lamp and RTA. We will make clear the similarities of photoluminescence with the way of preparation techniques.